1. Field of the Invention
The present invention relates to dental compositions, more particularly, the present invention relates to tooth filling compositions, that are curable in two curing steps.
2. Discussion of Related Art
Essentially all commercial dental compositions which meet the high cosmetic standards, especially tooth filling compositions, consist of synthetic resins which contain organic or inorganic fillers (the so-called composites). The proportions of these fillers may vary from 30 to 90% by weight. In particular, in the field of the so-called side tooth composites, it has been proved desirable to incorporate the maximum amount of hard inorganic fillers in tooth filling compositions in order to characterize the final restoration with sufficient hardness. In particular, the use of silanized, finely granular fillers, such as quartz or X-ray-opaque glass, have proved to be especially advantageous for preparing abrasion-resistant side tooth composites. Such tooth filling compositions favorably contain from 80 to 90% by weight of an inorganic filler material. The fillers normally employed have an average particle size of from 1 to 15 .mu.m. Conventionally, substantially finer fillers within the range of from 0.02 to 0.05 .mu.m are employed together with the above mentioned fillers in order to render the compositions sufficiently plastic.
It has been found to be particularly advantageous to employ the so-called hybrid composites in the side tooth composite area, because with the simultaneous use of from 5 to 25% by weight of filler particles having an average particle size of from 0.02 to 0.05 .mu.m and from 65 to 85% by weight of filler particles having an average particle size of from 1 to 15 .mu.m, especially abrasion resistant tooth filling compositions are obtained. In this connection it has been found that such side tooth composites possess sufficient hardness to resist wear inside the mouth for a sufficiently long period of time. On the other hand, the problem has arisen that after placing and curing the filling in the tooth, the curing normally effected with visible light, any existing excess can be distinguished from the surrounding tooth material only with difficulty. On one hand, this is due to the possible tooth-like coloring of the material, (in contrast to the classical amalgam filling), and on the other hand, this is also due to the tooth-like hardness of such hard tooth filling compositions.
A dentist encounters the same problems with laying tooth fillings, when cementing inlays, onlays, and facing shells made of sufficiently transparent material, e.g., porcelain or synthetic resin. At the present time, light-curing materials are preferably employed for these purposes, but which are subjected to partially to post-hardening, by a subsequent redox process. Since the initial fixing is invariably initiated with a photopolymerization, the problems, as in the placing of the tooth fillings, reside in the finishing off of these fillings, particularly in the finishing steps of removing the excess material and affecting occlusion by abrasion, these steps have become very difficult for the dentist, since these steps are very time consuming and cause a high wear of the polishing instruments. Accordingly, for this purpose, only very expensive diamond tipped instruments can be employed, and due to the use of such instruments, there is always an existing risk that, after the placement of the filling, the enamel rim, i.e., the marginal region of the existing tooth, is in danger of being damaged during polishing.
It is the object of the present invention to provide novel dental compositions, particularly tooth filling compositions, which are curable in two curing steps and which do not exhibit the drawbacks of the prior art. In particular, the new dental compositions are easily processable and when cured, are characterized with an excellent final hardness of the dental material.